The present invention relates to a reduction ratio control in a continuously variable transmission drivingly connected to an engine of a vehicle having an accelerator manually operable by a driver of the vehicle.
A continuously variable transmission is known which has a stepper motor as an actuator and hydraulic arrangement for varying a reduction ratio in the transmission from one ratio state to another ratio state in a continuous manner in correspondance with one operating position and another operating position taken by the stepper motor. The stepper motor is controlled in response to an output signal generated by a control unit. It is known to control the continuously variable transmission in a feedback or closed loop manner based on a deviation between an actual value of a turbine (or input) revolution speed and a target value of the turbine revolution speed by controlling the operating position of the stepper motor in such a direction as to reduce the deviation toward zero. According to this known control, it has been experienced that during downshift with power, an increase in output torque does not occur quickly, resulting in a sluggish response to the driver's power demand.
An object of the present invention is to improve a reduction ratio control such that an output torque increase takes place at an appropriate timing in response to a driver's power demand during downshift with power.